It is possible with current solutions to transmit audiovisual films and programs in digital form via broadcasting networks of the, cable, satellite, etc. type or via telecommunication networks of the DSL (Digital Subscriber Line) type or BLR (local radio loop) or via DAB (Digital Audio Broadcasting) networks, etc. Moreover, in order to avoid the pirating of works broadcast in this manner, these works are frequently encrypted or scrambled by various well known means.
However, the main disadvantage of current solutions such as in WO 01/65762 is that it is necessary to transmit not only the encrypted data to the users, but also the decryption keys. The transmission of the decryption keys can be made before, at the same time as or after the transmission of the audiovisual programs. In order to increase security and therefore the protection of audiovisual works against an ill-intended use, the decryption keys as well as the decryption functions of the audiovisual decoders can comprise improved security means such as smart cards or other physical keys that can optionally be remotely updated.
Thus, the current solutions applied to a set-top/decoder box with the possibility of the local recording of audiovisual programs in digital form on any support of the hard disk type or some other type of memory offers an ill-intentioned user the possibility of making non-authorized copies of the programs recorded in this manner, since at a given moment this user possesses with the digital settop/decoder box, whether associated or not associated with smart card systems, all the information, software programs and data permitting a complete decryption of the audiovisual programs. Precisely by virtue of the fact that the user possesses all the data, the ill-intentioned user will have the possibility of making illegal copies without anyone perceiving this fraudulent copy at the moment at which it is made.
One solution could therefore consist of transmitting all or part of a digital audiovisual program solely on demand (video services on demand) through a broadband telecommunication network of the ADSL, cable or satellite type without authorizing the local recording of the audiovisual programs. The disadvantage there is quite different and stems from the performances of these networks, that do not allow continuous streams of several megabits per second to be guaranteed to each user, as required by MPEG streams, that require bandwidths of several hundred kilobits to several megabits per second.
Under those conditions, one solution consists of separating the streams into two parts of which one can not be used by itself. WO 99/08428 teaches a process for the multi-application processing of an active, localizable terminal in which at least one connection is made to an identifiable program dedicated to carrying out an application, which program dictates its conditions of use to the terminal for making the functions available. The terminal communicates on an ad hoc basis by using a connection with the management center for the realization, if necessary, of the inputs and outputs of the capacities of the latter, which management center becomes a slave or does not become a slave of the terminal at the level of the application software relative to the entering program. That disclosure also concerns the process of identifying the program and the terminal in use. It divides the stream into one part identifying the user and into one part containing the program properly speaking. It is not unusable, but only locked by the first part. Finally, it does not present any solution for synchronizing the parts.
On the other hand, EP 0 778 513 describes a process permitting the prevention of the illegal use of information by adding control information to verify the rights of the user. The system permits the permanent knowledge of which part of the information is being used and by which user and consequently to know if the user is illegal or not. That process thus secures the data by adding additional information that denatures the initial information.
WO 00/49483 also offers processes and systems for creating a connection between the users and an editor of digital entities. The process comprises at least one of the following steps: subdividing the digital entity into two parts; memorizing one part in a memory zone of the server connected to a computer network; transmitting the other part to at least one user with computer equipment; connecting the computer equipment to the computer network; establishing a functional connection between the first part and the second part. These processes and systems do not specify on the one hand if the memorized part on the server can be stored by the user, which would permit pirating of the digital entity, and on the other hand do not specify the manner of synchronizing these two parts.
U.S. Pat. No. 5,937,164 uses a solution consisting of separating the stream into two parts of which the smallest one contains information necessary for using the largest one. However, it is not sufficient for responding to the problem identified. In fact, suppression of one part of the stream denatures the format of the stream and it can therefore not be recognized as a standard stream that can be used with general software applications. That process simultaneously necessitates a specific software on the server side for the separation of the two parts and another specific software that assures not only reconstruction of the stream, but also acquisition of the main stream and its use according to a format proprietary for the solution. The proprietary format is not the initial format of the stream before separation into two parts in that solution.
U.S. Pat No. 5,892,825 resumes the preceding patent, but in a narrower scope because the streams in it are always encrypted. U.S. Pat. No. 6,035,329 is based on the same principle and concerns a process permitting reading a disk of the CE-ROM or DVD-ROM type conditioned by the identification of the rights by inserting a smart card on which the information necessary for reading is stored. That process is still not sufficient because it does not guarantee that the modified stream has the same format as the original stream. U.S. Pat. No. 6,185,306 concerns a process for transmitting encrypted data from a web site to a requesting computer. However, that process allows the user to have all the tools necessary for copying the data at a given moment.
WO 00/44172, discloses a system of video distribution on demand consisting of transmitting encrypted video streams from a supplier to one or several receivers. The encrypted video is stored in advance in the receiver and displayed at a later date. The display request is addressed to a video sender that sends the decryption information for an immediate display of the video stream. The decryption information is sent to the receiver via a separate path or via the same path as the encrypted video. Before sending the keys (static or dynamic) for the decryption a step for the identification of the receiver is carried out. This prior art therefore describes a system of encryption with the aid of a key or keys that is well known. However, the entire video stream protected by encryption is stored in the receiver and the data set of the video stream is located inside the protected video and is therefore vulnerable to being pirated.
U.S. 2002/0164024 A1, concerns a system for processing video and audio data based on a relation of prediction between frames, containing a module for fragmentation of the data, a module for encryption of part of the data, a sending module, a module for differentiating the processing by type of frames I, P, B and their classification in separate files, a receiving module, a decryption module and a module for assembling data. The encryption process is carried out solely on fragments comprising images I, that are decrypted and reassembled in the receiver, thus reconstituting the video, which reconstitution is carried out by aligning packets in increasing order of the time reference indicated in the binary stream. It describes a system of “classic” encryption with optimization of encryption. The fragmentation is applied to separate the I images from the rest of the stream to encrypt them. After this selective encryption, the fragments are sent using different queues. However, all the data of the audiovisual stream remain inside the protected stream with all or part of the stream not being encrypted.
WO 01/97520 also teaches methods, processes and devices for controlling the transmission and recording of digital content of the MPEG-2 type. However, it does not teach any specificity for synchronization the streams constituting the two parts of one and the same audiovisual program. Moreover, that method is totally ineffective for low bandwidth telecommunication networks because it substitutes all or part of the I images, whose weight in bytes is very expensive during transmission of the second stream.